Free flowing bulk materials, such as granular products and liquids, are commonly stored and shipped in large bulk bags. These bags are typically made of air pervious, flexible woven materials. For many types of bulk products it is necessary to line the interior of the fabric bag with an air and liquid impervious liner. Typically these liners are made of plastic sheet material such as polyethylene.
Being flexible, bulk bags tend to bulge outwardly when filled with bulk materials. When this occurs their shape changes from squared off or rectangular to round. When this occurs they become difficult to handle and to store with spacial efficiency.
Attempts have heretofore been made at solving the problem of bulging. This has mainly been done by incorporating upright panels that bridge the insides of the bag corners. Examples of these are shown in U.S. Pat. Nos. 4,834,255, 5,071,025, 5,222,812, 5,328,267, 5,468,528 and 5,538,155. Though these corner panels do reasonably well in limiting bulging, they are costly to manufacture. Also, sometimes the corner spaces located behind the panels are slow to fill and are incompletely filled with bulk materials, even though they do have holes. When this occurs the full capacity of the bulk bag is not used.
Accordingly, it is seen that a need remains for a bulk bag with liner that is relatively easy and economic to produce and effective in restricting bulging without limiting fill capacity. It is to the provision of such a bulk bag and method of producing such a bag that the present invention is primarily directed.